Method of sintering metal



Dec. 31, 1940- B.'BERGHAUS ETAL 2 7 I METHOD OF smmune METAL Filed April 22. 1939 l'ivvfigr Illlllllll 3.3. 65mg M hQBur ham} Patented Dec. 31 1940 UNITED STA ATENT OFFICE ma'rnon or smaanvo METAL Bernhard Berghnlll, Berlin-Lankwltz, and Wuhelm Bnrkhardt, Berlin-Grnnewald. Germany; said Burkhardt asslgnorto said- Berghaus Application April 22, 1939. Serial No. 289,550

- In Germany April 30, 1938 3 Claims. (CI. 75-22) This invention relates to a method of manufacture of sintered bodies from metal powders, or from powders of hard material or their mixtures, the characteristic feature of which is-that 5 the articles of pressed powders are subjected to an electric gas or glow discharge at reduced pressure or in vacuum, connected as an anode or neutral, for the purpose of being heated.

The metal wall pf the vacuum sintering chamher is preferably connected as a cathode. An electrode introduced in an insulated and screened manner may serve asthe anode. The pressed articles or sintered material are preferably ar-v ranged on a metal support which is introduced into the vacuum sinterlng chamber in an insulated and screened manner. The metal support is preferably made hollow and cooled from the inside. The plate or supports on which the.

sintered materialrests may be made of metals having a high vmelting point. suchas chromium. tantalum. titanium, molybdenum, tungsten or the like. The plate or the supports on which the' sintered material rests may, however, consist of other materials having a high melting point, such 26 as sintered earth", for instance beryllium oxide,

zirconium oxide, thorium oxide or the like, but

V also of graphite. The electric gas discharge may,

be produced by means of a direct or alternating current voltage.

$0 1 When'an alternating current voltage is applied to the path of the gas'discharge one terminal of the source of alternating current voltage is connected to the wall of the casing-andthe other terminal of the source of alternating current ac voltage to the current lead-in which isin conductive connection withthe bodies to be 'or to an electrode which .is insulated with respect thereto. 1

" The gas discharge remiired for the sint'erins I 40 is preferably operated at a pressure of 40 to 0.01 and, preferably 5 to 0.1 millimeters of mercury.

The flllinggas for the gas discharge for-- instance. consist of'hydrogen, ni f t n. ammonia,

hydrocarbons or raregases. The voltage which is to be applied to the discharge path may. ac ord ing to the desired heating-up and theadiusted .vacuum. be 400 to 10,000 volts; In most cases voltages up to 5,000 volts suflice.. The energy to he introduced is dependent upon the .sine andfio thenumber of thepressed artlclestob'eheated andthe temperature to which the articles are to;be subjected. In order to obtain aintered -temperaturesupto 1000 C.adiaehargemergy uptobwatts-persquarec'entimeterofsurlaeeof 65 the cathode may for instance, be aethis case-use may be made'of-any of the mixtures known per se in the manufacture ofhard metals.

cording to the filling of the men. In the case of temperatures up to 2000 C. and over3000 C. up

to and more wattsper square centimeter of surface of the cathode isrequired according to the size of the body to be sintered;

The screening around the conductor is essential for the introduction of large energies at the stated voltages. The screens are arranged at such a distance'around the conductor that no discharge can take place in the intermediate 10 space between the conductor and the screen,

The screen is provided around the conductor over such a distance, and preferablyln a labyrinth form, that charge'carriers, such as ionlsed gas particles or vaporised 'metal from the treatment 15 chamber cannot reach the insulating and sealing material. The insulation and the sealing may be two different materials or use may be made of one material having the'two properties. The

insulation and sealing are preferably provided 20 aluminium or heavy metals, such as iron, copper, .and cobalt. 'As regards-hard materials, more particularly for cutting tools, hard metal car- .5

bideahard metal silicldes, hard metal nitrides. hard metal borides come into question, alone or in admixture with auxiliary metals. such as aluminium, iron. nickel, cobalt and the like. In

By evacuating the treatment chamber thearticles formed of pressed metal powder are subiected to anextensive liberation of gas before --'the heat comes-into action, the removal of gas being carried out upto the vacuum which can I be technically obtained. Upon the voltage being applied to the electrodes and the filling gas for thedischargebelngintroducedintothechambenoo which'flllingg'asmay havea-reducingzcarbonis .ing, entangling or indifferent actlomthepressed article-is heated'to the desired temperatu slowlyorouickl'yeecordingtothemateriaL-In aomecaees' it hubemfoundan advantage told cracking and while keeping their shape.

2 maintain certain definite temperatures and then to further heat the article.

without affecting the shape and the strength of the article.

The drawing illustrates a sintering oven for the manufacture of sintered bodies of metal powders or hard materials, in which the articles of pressed powders are subjected to an electric gas discharge at reduced pressure or in vacuum connected as an anode or neutral, for the purpose of being heated.

The sintering oven consists of a lower metal part i and a removable upper metal part 2, which are connected together in a vacuum-tight manner by the sealing 3 which consists, for instance, of two packing rings. The removable upper part is provided with a cooling jacket 6 to which a medium is supplied through the pipe connection 5, being discharged through the pipe connection 6. The upper part is provided with an insulated and screened inspection window I arranged in a metal sleeve 8, which is irsulated with respect to the pipe connection Ill by means of washer 9.

The metal sleeve 8 is spaced from the pipe in to provide a narrow protective gap H. The inspection window is secured in position by the ring l2 of insulating material and by means of screws,

not shown.

- The lower metal part is provided with cooling passages l3 and supports a central metal lead-in It which is insulated and screened and capable of being cooled and to which a cooling medium is supplied through the pipe l5, being discharged through the pipe IS. The lead-in It carries an electrically conducting or insulating screening hood or plate H, for instance of metal orinsulating material, which serves to support the material IS to be sintered, for instance through the interposition of metals or insulating bars 89.

The material 19 to, be sintered'may be connected as an anode or remain neutral. The oven'isprovided with an auxiliary electrode 20 which ineludes two parts and is introduced in an insulated and. screened manner. The conductor i4 and the auxiliary electrode structure 20 are sealed and insulated with respect to the housing by means s of insulating and packing rings 2| and 22. The

asere'ws (not shown).

insulating and sealing assembly is provided with a disc 23 of insulating material by which the assembly" may be clamped to the housing with Between the metal lead-in i ii and the auxiliary electrode 20 and betweenthe latter and the metal wall of the bottom there are provided narrow screening gaps 2t and 25.

.The pipe connection 26 serves for the supp y of V a filling gas, such as hydrogen, nitrogen or the.

1 likein a regulated amount. The sieve 21 preassmvv vents the gas discharge used for the heating or sintering from br throu h into the supply pipe. The pipe connection 28 serves to connect a vacuum pump by means of which a pressure of 40 to .0.01 and, preferably 10 to 0.1 millimeters of 5 mercury, is maintained in the sintering oven. The sieve 29 prevents the gas discharge from breaking through into the pipe leading to the vacuum pump.

The source 30 of continuous current is connected with the negative terminal thereof to the metal wall of the chamber of the oven through a switch 3| and with the positive terminal through a'switch 32 and a resistance 33 or an inductance coil 36, either through the switch 35 to the current lead-in It for the sintered body or through the switch 36 to the auxiliary electrode 20. If a source of alternating current is employed for creating the glow discharge, the secondary 31 of the supply transformer is connected at one end through the switch 38 to the metal wall of the sintering oven and at the other end to the switch 82. The alternating current voltage may be impressed across the metal wall i and the lead-in it or-the auxiliary electrode 20 by closing the switch 38 and either of the switches 35 or 36.

What we claim is:

1. A method of manufacturing relatively hard metal articles from metal powder which comprises, pressing the metal powder into the desired article shape, supporting the shaped metal sealed electrically conducting-housing, evacuat- 4'5 ing the housing to remove gases therefrom, introducingan inactive gas into the housing, and impressing a voltage across the housing and the article with the housing serving as a cathode and the article serving as an anode to create a glow go discharge within the housing which envelops the article tolsinter the pressed metal powder.

3. A method of manufacturing relatively hard metal articles from metal powder whichcomprises, pressing the metal powder into the de- 5| sired article sh'ape,-supporting the shaped metal 'powder'within and insulated with respect to a sealed electrically conducting housing, evacuating the housing to remove gases therefrom, introducing an inactive gas into the housing, and creating a glow discharge within the housing with the housing connected asa cathode for the glow discharge. whereby the glow dischargeenvelops the shaped metal article to sinter the pressed metal powder. f

' BERNHARD BERGHAUS.

WILBIEIM B. 

